Method of grinding propeller shanks



Nov. 2, 1948. F A, GRUETJEN 2,452,926

l METHOD OF GRINDING PROPELLER SHANKS l Filed July 15, C1945 2 sheets-sheet 1 2 sheets-sheet "a F. A. GRUETJEN' METHOD OF GRINDING PROPELLER SHNK-S Nav. 2, 1948., v

Filed July 15, 1945 Patented Nov. 2, 1948 Vivm'l,7.11011 0F GRINDING 'P noPELilER sHANKs Frederick A. Gruetjen, Milwaukee, Wis., lassgnorto A. O. Smith Corpora-tions Milwaukee, Wis., a corporation of New York Application July 13, 1945, Serial No. 604,771

This invention relates to propeller shanks.

Modern aircraft propeller blades have shanks of Various shapes, usually embodying a rlurality of external and internal circumferential ribs, shoulders and grooves for accommodating balancing weights and for securing the blade to the'hub attachment. In orde-r to, preserve the proper dynamic balance of the blade in operation and prevent unbalan-ce of the propeller, the internal and external surfaces of the shank h-ave to be Inachined or ground with considerable accuracy relative to the longitudinal -center line of the blade.

In practice in the best known propeller factories, it has been the custom to mount the blade in a. shuttle w-hich is rotated on rollers .in a semicenterless grinding machine with rotary grinding wheels for grinding `the inside and outside of the shank, respectively; Shuttles are extremely expensive, and the loading and unloading of blades therein is along and tedious oper-ation greatly reducing the capa-city of the plant unless a large number of shuttles, machines and skilled workmen ar-e available. Furthermore, the rotation of the shuttle becomes inaccurate in the event dirt or foreign material collects upon the supporting rollers.

The object of the present invention is to eliminate the use of shuttles and provide a simpler and less costly method of grinding the shanks.

Another object is to provide a more accurate method for grinding propeller shanks.

The practice of the invention is illustrated in the accompanying drawings in whi-ch:

Figure l is a longitudinal central section taken through the shank end of a propeller blade after rough machining and prior to grinding;

Fig. 2 is a side elevation of a hollow spindle grinder with parts in section and showing .the mounting of a blade preparatory to grinding ythe inside of the shank;

Fig. 3 is a perspective View showing the blade mounted on an expanding chuck in a standard lathe;

Fig. 4 is a longitudinal central section taken through the shank end of the blade after completion of the grinding operation; and

Fig. 5 is a similar section after threading.

The blade I to be ground is hollow and has a generally cylindrical shank 2 merging. into .the air foil body of the blade, and a tip centering projection 3. The projection 3 has a tapered centering punch mark or recess 4 located in its tip and on the longitudinal -center line of the blade Vas determined in a vertical balancing machine for dea method of grinding 2 Claims. (Cl. L51e-2.90)`

2 l termining lthe cen-ter of gravity. The shank -c'f the :blade is ordinarily machined inside and outside on the measuredlongitudinal centerline of the blade prior Ito-balancing, and leaving an allowance for lgrinding on all surfaces. l

The blade `thuis lfabricated is mountedin a hollow spindle grinder 5` as shown in Fig. The hollow spindle 6 of the grinder has a chuck or collet I at its forward end for centrally securing the cylindrical shank 2. The jaws of the. chuck I should grip the shank at about the longitudinal mid-.point of the proposed internal grinding -operations.

The centering projection 3 at the tip of the blade is engaged by a spring pressed centering pin 8 which is rotatably mounted `in a stationary post 9.

The grinder I 0 comprises a small high speed contour grinding wheel II mounted on a .shaft I2 driven by a motor I3 on a Apedestal I4 which can be moved longitudinally toward and away from the blade. The grinding wheel Il enters the shank and engages the inside surface eccentrically of the shank to effect grinding of the same. The Wheel I I is replaceable by wheels of different shapes and sizes :to enable the grinding of different types of Shanks. The inside grinding may be accomplished with a single Wheel or `different wheels may be employed.

The grinding wheel II is fed longitudinally in the shank as it rotates, and the rotation of th-e shank taken with the eccentric mounting of the wheel II relative to the center line of the shank effects a relative grinding feed circumferentially of the shank.

The grinding operation illustrated .provides an end shoulder I5, a cylindrical surface I6 for threading, a grooved relief I'I at the inner end of I6, and an inner shoulder I8 for retaining the balancing weights. Different types of blades will have a different contour.

After the inside grinding is completed, the blade is removed from the machine of Iig.` 2 and mounted in the machine of Fig. 3 which may be a lathe as shown or a grinder. Here the blade is supported for rotation on an eXpansible mandrel I9 which engages the inside of the shank and thereby accurately locates the blade for rotation on its longitudinal center line. The mandrel should be of a type that will not mar the inside surface of the shank. A grinding wheel 20, mounted on a pedestal 2l, is fed to and along the outsideof the shank as the latter rotates.

Usually two separate grinding wheels are employed. The rst grinding wheel trues the cylindrie-a1 surface of :the shank from the end to a suitable distance beyond the cuff ring 22. The second grinding Wheel is contoured to provide the grease seal relief 23. Dilerent typ-es of blades will require different outside shapes for the shanks.

By employing the :method above outlined, the production of 4bla-des is'greatly increased with less equipment -andlabor than under former practices which employed 'a shuttle grinder. The accuracy of grinding is more readily maintained than is possible with shuttles, since all of the rotary bearings are enclosed and protected from dirt, and the mounting of thev blade is ordinarily more accurate.

Various practices may be employed within the scope of the invention as set forth lin the accom panying claims.

I claim: y 1. The method of grinding hollow propeller blade shanks, comprising mounting the :blade in a hollow spindle grinder with a -chuck or collet gripping the shank at about its mid-portion, een? tering the blade in the spindle by applying an index holder to the tip -of the blade, grinding the inside contour of the shank to nished dimensions, removing the 4blade and mounting the sameupon an expansible rotary mandrel engaging the accurately ground inside surface of the shank, and

i 4 then grinding the outside of the shank to accurate dimensions.

2. The method of grinding hollow propeller blade Shanks, comprising mounting the blade in a hollow spindle grinder with a chuck yor collet gripping the shank, centering the blade in the spindle by applying an index holder to the tip of the blade, grinding the inside contour ofthe shank to finished dimensions, removing the blade and mounting the same upon an expansible rotary mandrel engaging the accurately ground inside surface of the shank, and then grinding the outside of the shank to accurate dimensions.

FREDERICK A. GRUETJ EN.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number 

